This application is a continuation-in-part of application Ser. No. 674,098, now abandoned, the continuation of which, Ser. No. 018,597, issued as U.S. Pat. No. 4,714,340.
At high speeds, greater than 500 feet per minute (fpm), no known method or device exists which will reliably allow an operator to visually inspect the total product for conformity to a standard and to discover defects which sometimes occur in the printing process. Products requiring such inspection while traveling at high speeds include variously printed and coated webs, and continuous motion folding and closing operations. Prior art devices are particularly unable to inspect materials that are subject to stretch or are not printed with a symmetrical copy.
Inspection systems which employ "spot" strobe lights are inadequate because of an unduly limited viewing area. Furthermore, spot strobe light inspection systems are timed to provide a fixed or locked image and do not provide a pan or scroll mode whereby the operator can view images across an entire web under the optical illusion that the images are moving slowly through the field of view.
Revolving mirror devices, because of physical limitations, must operate parallel to web direction of movement and are realistically limited to web speeds of 500 fpm and below. Functional limitations preclude observing the web at 90.degree. to its direction of travel and thus prevent the inspection of short repeats, typically under 5 inches.
Because of the above and other limitations in the prior art, there is a need for a more efficient, convenient and practical method and apparatus for visually inspecting high speed printed webs and the like, especially in situations in which the images are not symmetrically spaced around the press cylinder, in situations where there is no correlation between the printed image and the printing press drive, or when elastic or other materials subject to stretching are used as the web. The broad objective of this invention is to satisfy that need in a comparatively simple and economical manner.